In the biomedical field, the development of thromboresistant materials is hindered by the interaction of the blood itself with artificial surfaces. In normal situations, platelets or blood components do not adhere to the vasal lumen, whereas the contact with a synthetic material causes platelet deposition, often together with thrombotic phenomena. Accordingly, polymeric surfaces, which show the ability of inhibiting the formation of thrombus, are of great interest for the preparation of cardiovascular protheses and devices to be used in contact with blood.
Antithrombogenic surfaces can be divided into three main classes:
I) Surfaces promoting the formation of neointima, since they have adhesive properties for endothelial cells. Antithrombogenicity is due to the functional capacity of the cells themselves. PA0 II) Surfaces capable of blocking the thrombus formation, therefore inhibiting: PA0 III) Thrombolytic surfaces.
a) platelet aggregation or activation; b) fibrin network formation. PA1 [D] is C.sub.1 -C.sub.12 straight or branched alkylene unsubstituted or substituted with one or more hydroxy groups, optionally interrupted by oxygen atoms, or [D], together with N' and N", forms a piperazine ring, in which case R.sub.1 is absent; PA1 [E] is C.sub.1 -C.sub.12 straight or branched alkylene unsubstituted or substituted with one or more hydroxy groups, optionally interrupted by oxygen atoms; PA1 R.sub.4 -R.sub.9 are independently hydrogen or methyl. PA1 R.sub.3, R.sub.4 and R.sub.9 are methyl, R.sub.5 -R.sub.8 are hydrogen, a and b are 1, c is about 8.5, d is 0, the sum e+f is about 2.4; PA1 a, d, f are 0, b is 2, c and e are 1, R.sub.4 -R.sub.7 are hydrogen. Particularly preferred are bisacryloylpiperazine (BAP), methylene-bis-acrylamide (BAC), dihydroxyethylenebisacrylamide (DHEBA). PA1 [G] is C.sub.2 -C.sub.12 straight or branched alkylene, unsubstituted or substituted with one or more hydroxy groups, optionally interrupted by oxygen atoms and/or &gt;NR.sub.10 amino groups, wherein R.sub.10 is hydrogen or C.sub.1 -C.sub.4 alkyl.
Surfaces belonging to the second class are particularly important from a technological point of view, and the present invention refers to this field.
Antithrombogenic materials must have one or more of the following requirements:
1. Low critical surface tension;
2. Negative surface charge;
3. Hydrated polymeric surface at the interface with blood;
4. Heparin binding capability, either by covalent or ionic bond, or heparin controlled release capability.
5. Capability of selectively adsorbing "passivant" blood proteins, such as albumin, or of interacting with blood elements (endothelial cells) without activating coagulation processes.